Altered cytosolic Ca2+ dynamics in cultured Guinea pig cardiomyocytes as an in vitro model to identify potential cardiotoxicants

Altered intracellular calcium (Cai2+) handling by cardiomyocytes has been implicated in drug-induced cardiomyopathy and arrhythmogenesis. To explore whether such alterations predict cardiotoxicity, Cai2+ imaging was conducted in cultured, spontaneously contracting Guinea pig cardiomyocytes to characterize the effects of 13 cardiotoxicants and 2 safe drugs. All cardiotoxicants perturbed Cai2+ at therapeutically relevant concentrations. The cytotoxic chemotherapeutics doxorubicin and epirubicin, known to cause cardiomyopathy, preferentially reduced Cai2+ transient amplitude and sarcoplasmic reticulum (SR) Ca2+ content, whereas Torsade de Pointes (TdP) inducers and potent hERG channel blockers (amiodarone, cisapride, dofetilide, E-4031 and terfenadine) predominately suppressed diastolic Cai2+ and contraction rate, and prolonged Cai2+ transient duration. The molecularly targeted cancer therapeutics, sunitinib and imatinib, exhibited profound effects on Cai2+, combining effects of cytotoxic chemotherapeutics, TdP inducers and potent hERG channel blockers. TdP inducers lacking direct hERG inhibition, ouabain and pentamidine, significantly elevated Cai2+ transient amplitude and SR Ca2+ content while aconitine primarily accelerated automaticity and elevated diastolic Cai2+ similar to ouabain. Finally, amoxicillin and aspirin did not exert any significant effects on Cai2+ at concentrations up to 100 μM. These results suggest that detecting altered Cai2+ handling in cultured cardiomyocytes may be used as an in vitro model for early cardiac drug safety assessment.